Resistance welding of a first metal member to a second metal member (also known as electric-resistance welding) is a known metallurgical process wherein the first and second metal members are heated by their own electrical resistance to a semi-fused or a fused state by the passage of very heavy electrical currents through the members for very short lengths of time, and are then welded together, by forcing the first and second members together under pressure while the welding current is applied across the members. Resistance welding has many advantages in efficiently and effectively providing consistently reliable welds in high-volume manufacturing operations, when compared to alternative brazing or welding methods using gas torches or electrical arcs.
In order to achieve a complete resistance weld of the interface between the two mating members, the members must fit together very tightly at the interface at the time welding current is applied. The need for having the members fit together tightly, makes it so difficult to economically resistance weld together thin-walled metal members, in the form of sheets, tubes, or similar shapes, in high-volume production, even where the configuration of the members is fairly simple, that such members are typically brazed or arc welded together rather than being resistance welded.
For example, in the past, prior to joining a metal sheet to a tube intersecting the sheet at an angle, the mating edges or surfaces of the members to be joined had to be cut or prepared along a three-dimensional contour so that the intersection between the members would fit together tightly enough before welding to allow a good weld joint to be made. This can be very difficult to achieve in thin-walled members that tend to flex under the pressure of the tooling used for preparing the mating edges or surfaces. The manufacturing costs for preparing the edges of the members to achieve an acceptably tight fit before welding, together with the cost of engineering for designing the members themselves and the equipment used for machining the members to achieve a tightly filling interface is undesirably high.
In addition to the cost associated with machining the members, complex fixtures were required in the past to hold the members in position and to apply pressure along an interface, which is often three-dimensional, during resistance welding of the interface.
Commonly assigned U.S. patent application Ser. No. 09/969,066, titled “Method For Metallurgically Attaching Together Two Members” by Ananthanarayanan, et al, which is incorporated herein by reference, provides a method for resistance welding together an interface between two annular shaped members having one member fitted into a hole in the second member. One member includes a through hole having a longitudinal axis and first and second longitudinal ends, and a longitudinally projecting flange surrounding the hole. The second member includes a solid transversely-projecting annular rim. The second member is partially disposed through the hole in the first member with the flange of first member projecting away from the rim of the second member, and applying clamping pressure and electrical current through electrodes to form a weld, wherein after the weld is created, the rim of the second member is seated on the first member at the first longitudinal end of the through hole. The method may be used for second members fitting into the hole in the first member with either an interference or a non-interference fit between the first and second members. The electrodes may be used for longitudinally compressing the transversely-projecting solid annular rim, and transversely compressing the longitudinally projecting flange during the welding process to achieve a fit tight enough for a high quality resistance weld to be made at the interface between the first and second members.
While the approach disclosed by Ser. No. 09/969,066 to Anananthanarayanan, et al, works well with certain annular shaped members, such as tubes, and alleviates many of the problems described above, further improvement is desirable to allow resistance welding of non-annular shaped members, and to further facilitate resistance welding of thin-walled annular shaped members.
What is needed, therefore, is an improved method for resistance welding of thin-walled sheet metal tubes and similar shapes.